1. Field of the Invention
The present invention relates to a microorganism testing device measuring microorganisms included in foods.
2. Description of the Related Art
Conventionally, there have been known measuring devices which execute various kinds of methods for quick and simple measurement of the number of viable bacteria. Especially, a device for measuring the number of bacteria has become of major interest as a technique for quick and direct measurement of the number of viable bacteria, wherein the device uses a fluorescence flow cytometry method.
The fluorescence flow cytometry method is a particle measuring method, in which the diameter of specimen flow including specimens dyed with a fluorochrome is made smaller, and the specimen is discharged in a flow one by one for measurement. A device for measuring the number of bacteria, which uses the above method, may measure a specimen one by one in a short time.
Moreover, in the fluorescence flow cytometry method, the diameter of the specimen flow is made narrow down by forming a laminar flow of a specimen and sheath liquid for making use of a pressure difference between those of two liquids in order to prevent elements in the specimen from adhering to the wall of the flow path.
Furthermore, in order to implement the method with a low cost, or to eliminate washing processing, there has been known a method in which a flow path portion used for measurement by the fluorescence flow cytometry method is made into a disposable chip, so that the flow path portion to be measured is disposed of without being re-used after measurement being made in the disposable chip. The method has been described in, for example, a Journal of Biomolecular Techniques, Vol. 14, Issue 2, pp. 119-127.
In the above-described technology, it has been required, when the number of viable bacteria included in foods is measured, to remove residual food from a specimen before a tester injects the specimen and sheath liquid into a well of the chip, because it has not been considered that measurement of bacteria is rapidly executed for various kinds of food specimens.
Moreover, the flow cytometry method has required large residual food included in a specimen to be removed in a complete manner because a specimen including bacteria is poured into a flow of the sheath liquid from a thin nozzle with a diameter of about 100 μm.
Moreover, both reaction between a specimen and a dyeing reagent as batch processing, and measurement by the fluorescence flow cytometry method as flow processing are required to be compatible with each other in a disposable chip. Accordingly, a container (hereinafter, called a reaction container) in the chip for reacting liquid mixture of the specimen and the dyeing reagent is required to have two conflicting functions. That is, one is a function by which, when reacting, a liquid mixture is prevented from flowing into a detection flow path from the reaction container, and the other is a function by which, when measuring, the whole quantity of the liquid mixture is securely delivered from the reaction container to the detection flow path.
Furthermore, small impurities also have a possibility to exert an unfavorable influence upon measurement results, for example, because the impurities produce auto-fluorescence. Accordingly, it is indispensable for the small impurities to be removed when the device is required to stably be operated. For example, when a bacteria is measured using fluorescence, a material, such as a pigment and chlorophyll, having auto-fluorescence property, and a cell which, by a fluorescent reagent, emits fluorescence similar to that of a bacteria are considered as impurities with a difficulty in distinction from the fluorescence caused by the bacteria. As the pigment and the chlorophyll are much smaller than the bacteria (about 1 μm), and an animal cell and a plant cell are much larger than the bacteria, complex operations are required to extract only the bacteria. These operations are complex in the same manner as the dyeing operations to require a professional skill.